Electron discharge device



M 12, 1935- L. H. BEDFORD Ef AL l,99 3,769

ELECTRON DISCHARGE DEVICE Filed Feb. 6,1932

. LQHBEDRQRD INVENTORS a G Arm/ems? Patented Mar. 12, 1935 ELECTRON DISCHARGE DEVICE Leslie H. Bedford and Douglas G. Coveney,

Aldwych, London, England, assignors to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application February 6, 1932, Serial No. 591,392 In Great Britain March 5, 1931 3 Claims.

, This invention relates to electric discharge devices and more particularly to electrode structures for thermionic vacuum tubes.

In vacuum tubes, it is frequently necessary to provide insulating or supporting members for certain electrodes. An instance of such members occurs in vacuum tubes in which the ends of the electrodes remote from the pinchare supported by each other, or by a wire or the like sealed into the pinch, an insulating member then being provided in order to maintain the remote ends of the electrodes in correct spacial relation. Typical forms of such members are: glass beads, mica or like bridges and metal plates provided with insulating bushings. All of these are subject to the disadvantage that the insulation resistance is apt to be lowered by deposits of conducting material which are vaporized from various parts of the tube either during manufacture or during the life of the tube. For instance, if the exhausting of the tube is accomplished with the aid of a getter, such as magnesium, a coating of conducting material may be produced on the insulating members, with the result that a path of not negligible resistance is produced between the electrodes engaging with the insulating member. The efficiency of the tube is thus impaired.

The production of such conducting deposits during the life of the tube is perhaps of great seriousness, since the effective life of the tube will be greatly diminished, although from the point of view of filament activity, a much larger actual life could be attained if the production of such conducting deposits were prevented.

Accordingly, it is an object of the invention to provide insulating or supporting members for vacuum tubes in which conducting deposits have no effect upon the insulation resistance of the members or upon the effective life of the tubes.

In accordance with the invention, it is proposed to employ an insulating spacing member for the electrodes of vacuum tubes which is so constructed that the essential insulating path contains a portion which is shielded from conducting deposits from other parts of the structure.

A feature of the invention resides in an insulating member comprising two strips of mica or other suitable material arranged as an electrode insulating member, one of the strips acting as a shield for the other.

A further feature of the invention is an insulating bush for inserting into a spacing or supporting plate, in which the bush is shielded against conducting deposits either by suitable design of the bush itself or by means of suitable shielding members.

These and other features of the invention will be more fully understood from the following description, wherein reference will be made to the accompanying drawing in which:

Fig. 1 shows a known form of insulating support;

Figs. 2 and 3 show forms of supports according to the invention;

Fig. 4 illustrates a conventional form of bushing, and

Figs. 5 and 6 show forms of shielded bushes according to the invention.

Referring now to Fig. 1 the usual form of mica or like insulating and supporting member is indicated by A. B is a support for this member and C is a grid support which engages with A. It is readily apparent that a conducting deposit on the lower surface of A will cause conduction between the grid C and anode B, with the disadvantages above referred to.

Fig. 2 shows similar electrodes to those illustrated in Fig. 1, but embodying the present invention. The insulating and supporting member A engages with the supports B and C as before; a shielding member A is provided, suitably spaced from A by means of rivets, packing, etc., and the holes D in this shielding member are made larger than the electrode supports. The supports thus pass through the shielding member A without making contact with it. It will be clear that member A prevents the deposition of conducting material on A, and since the holes in A are sulficiently large to insure a space being left between itself and the electrode supports B and C, the fact that conducting material may deposit on the lower surface of A is of no importance.

The holes in the shielding member A may be made as small as is consistent with the feature of preventing contact between it and the electrode supports. The holes must be sufficiently large, however, to prevent contact between A and the electrode supports due to faulty assembly during manufacture or to displacement of the structure during use.

A complete insulating and supporting member of a preferred form is shown in detail in Fig. 3. The supporting member proper, A, is shielded by a member A, the two being spaced from each other by means of rivets F. It will be seen that the holes E are of smaller diameter than the holes D. The former are of such a size that the electrode supports B and C (Figs. 1 and 2) are held in position by the supporting member A while the latter are sufficiently large so that the electrode supports are out of contact with the shielding member A.

The rivet shown in Fig. 3 may, of course, be replaced by any other convenient fixing means, such as channel-shaped pieces of metal, not shown, around the edges of A and A. It will generally be preferable, whatever form of fixing is used, to space the two members from each other, so that a free path is provided between the supporting member and the shielding member.

In Fig. 4 a known form of insulating bush is shown, provided with a hole in which an electrode support fits. This type of bush suffers from the disadvantage that conducting deposits on its lower face and side cause conduction between the electrode support and the plate, usually of metal, in which the bush is inserted.

The bush shown in Fig. 5 overcomes this disadvantage. The lower portion G is adapted to shield the upper portion H, and since the hole in G is made too large for the electrode supports to come in contact with the conducting on the lower face of the bush, the insulation resistance will always be as high as that of the bush, and will not be lowered by conducting deposits. bush shown in Fig. 5 may be made in one piece.

Fig. 6 shows a similar shielding bush, but in this case the shield is made separately and is attached to the main bush H by any suitable The bushes shown in 5 and 6 are provided with a waist J in order that they may be easily fixed into a metal plate or the like. The holes in the plate may be made a few milssmallerin diameter than the stem H of the bush. on forcing the bush into the hole in the plate, provided the metal of the plate is not unduly 'stretched, the plate will engage with the waist J and the bush will thus be securely held.

The shielding members shown in'Figs. 2, -3 and '6 may be made from insulating material or from metal. The former is usually preferable because of its freedom from possible short circuits, but in some cases the shield may be of metal and adapted to act also as an electrostatic shield.

In the foregoing description, invention has been described particularly with respect to insulating and supporting members located in the tube remote from the pinch or stem. It will be obvious, however, that the invention may equally well be applied to the shielding of electrode supports adjacent the pinch or in any position in a vacuum tube.

What is claimed is:

1. An electrode assembly for an electric discharge device comprising a plurality of electrodes having supports extending beyond said electrodes, a spacing member having apertures through which said supports extend, said supports being engaged by said spacing member and held therein, a metallic shielding member located between said electrodes and said spacing member, said shielding member having apertures of larger diameter than the apertums in said spacing member, the shielding member apertures being coaxially aligned with the apertures in said spacing member so that all the electrode supports pass freely therethrough without engaging said shielding member, and separate means engaging said spacing and shielding members for holding said members in spaced parallel relation on said electrode supports.

2 An assembly for an electric discharge device having a stem, comprising a plurality of electrodes having supports extending beyond said electrodes, a spacing member engaging said supports remote from said stem to maintain the spacial relation between said electrodes, and a metallic electrostatic shield interposed between said electrodes and said spacing member, said shield having enlarged apertures through which the-supports of the electrodes pass freely.

3. Anassembly for a discharge device comprising a plurality of electrodes having supports extending beyond said electrodes, a spacing member engaging said supports and maintaining the special relation between said electrodes, a metallic shield interposed between said electrodes and said spacing member, said shield having enlarged apertures through which all the supports of said electrodes pass freely without engaging said shield, and spacing rivets suspending said shidd from said spacing member in parallel relation.

LESLIE H. BED'FORD. 1 DQUGLAS G. 

